Slurry particle size determination

ABSTRACT

Method and apparatus for determining the particle size distribution in a slurry in a grinding circuit with the method and apparatus operative in an online manner and at frequent intervals for effecting this determination. A high-speed computer is used to better control the operation of the circuit. Such particle size distribution, obtained through a determination of the cumulative percentage of solids in the grinder output slurry, is regulated in relation to the infeed of slurry material into the grinder as a predetermined function of the weight of new material introduced into the grinder unit circuit, the known particle size distribution of that new material from classifiers returned as infeed to the grinder and the calculated particle size distribution of that overflow material.

United States Patent Continuation of application Ser. No. 601,608, Dec.14, 1966, now abandoned.

(54] SLURRY PARTICLE SIZE DETERMINATION 14 Claims, 6 Drawing Figs.

52 u.s.c|. 241/20, 241/21..241/30,24|/34 s11 lat.C1. "Bonn/o0, B02c25/00[501FieldofSearch 241/15,

[56] References Cited UNITED STATES PATENTS 3,094,289 6/1963 FahlstromVALVE 3,114,510 12/1963 McCarty 241/34 3,145,935 8/1964 Wilson 241/243,352,499 11/1967 Campbell. 241/21 3,358,938 12/1967 Brown 241/21Primary Examiner- Donald G. Kelly Attorneys-F. H. Henson and R. G.Brodahl ABSTRACT: Method and apparatus for determining the particle sizedistribution in a slurry in a grinding circuit with the method andapparatus operative in an online manner and at frequent intervals foreffecting this determination A highspeed computer is used to bettercontrol the operation of the circuit. Such particle size distribution,obtained through a determination of the cumulative percentage of solidsin the grinder output slurry, is regulated in relation to the infeed ofslurry material into the grinder as a predetermined function of theweight of new material introduced into the grinder unit circuit, theknown particle size distribution of that new material from classifiersreturned as infeed to the grinder and the calculated particle sizedistribution of that overflow material.

SET POINT PATENTEDAUB 3m 3,596,839

SHEET 1 OF 4 SENSING DEVICE SENSING DEVICE COMPUTER FLOW CONTRO DENSITYSET PO|NT 20 SUPPLY GRINDER I6 MEASURMENT CYCLONE l CLASSIFIER i' i W".T

- 1 p u n 1- '1. I s0 s2 T ,64 66 T PRODUCTION PRODUCTION PRODUCTIONPRODUCTION GRmDER CYCLONE CYCLONE CYCLONE 1 CYCLONE CLASSIFIERCLASSIFIER CLASSIFIER CLASSIFIER t j a l 1 FIG.2

WITNESSES INVENTOR x45 9 W Richard Eu. Puimon PATENTEDAus 3m 3,596,839

sum 2 0r 4 I OVERFLOW MATERIAL UNDERFLOW MATERIAL *I LOG PARTICLE SIZE dFIG. 6

4---I OG K -'1 IOO% FINER COURSE LOG b LOG d FIG.3

PATENTEDAUB 3am $3,596,838

sum 3 0F 4 PERCENTAGE OF SOLIDS DETERMINING APPARATUS GRINDER COMPUTERROTATING FUNNEL 88 DEVICE OUT PUT COMPRESSED AIR SOURCE FIG.4

PATENTEUAUG 3|91| SHEET 4 UF 4 COMPUTER FLOW I2:- DENSITY ae-|+ a4 60DENSITY FLOW GRINDER FIG.5

SLURRY PARTICLE SIZE DETERMINATION The present patent application is acontinuation of an earlier-filed patent application Ser. No. 601,608,filed Dec. 14, 1966 now abandoned.

In the milling and grinding of mineral ores, it is desirable to know theparticle size distribution at frequent and regular intervals in order todetermine how the grinding operation is proceeding, to check theoperation of the classifiers and to ascertain whether liberation of thedesirable mineral elements has proceeded as intended.

It has been known in the prior art to takea sample of the output slurryfrom the grinding circuit and apply it to a device in diluted form, thesize and number of the particles being I counted by photoelectric orother methods. Another prior art particle measurement technique is towash the sample through a series of screens having different meshsizes,'and to then dry and weigh the amount of solid material retainedon each screen. 1

In the desired operation of the grinding mill, the particle size in theoutput slurry has to'be fine enough such that the right and desiredgrade is reached. If the particles are ground too fine, slimes areformed which inhibit flotation and cause valuable mineral to pass totailings. On the other hand, if the particles are ground too coarse thisresults in an inadequate separation of the desired mineral from the hostrock; It should be further noted that the subsequent flotation process,employing a coating agent such as lead xanthate which has a specialaffinity for metal sulfide particles and causes them to adhere to airbubbles, themselves produced by the presence of a frothing agent,requires a consistent particlesize distribution in the feed slurry foroptimum performance of the flotation process.

It is an object of this invention to provide an improved measurementmethod and apparatus operative to better determine the particle sizedistribution in the output of a mineral-grinding circuit where theoutput is contained in a form which is 1 adapted for sensing of thedensity and flow conditions thereof. It is another object of the presentinvention to provide an improved technique for the determination ofparticle size in the output of a mineral ore-grinding circuit, whichtechnique is better adapted for online operation with a'high-speed-computer for better controlling the operation of thegrinding circuit.

It is further object to provide an improved control method and apparatusfor the operation of a mineral-grinding circuit wherein a better controlof particle size distribution is obtained through a determination of thecumulative percentage of solids in the output slurry from thegtindingdevice.

Experimentation shows that the separation of solids fed to a fixedcyclone classifier is a function of the inlet velocity and particlesize. Thus, for a given output slurry from the grinder at a givendensity and inlet velocity, the fraction of solids in the overflow fromthe classifier cyclone to the total solids fed to the inlet of theclassifier cyclone is a measure of the percentage of solids which werebelow the corresponding'particle size or mesh number for that particularmineral ore. By varying the inlet velocity, the percentage at theparticle size corresponding to that new velocity mayalso be determined,and I repeatedly so on over the range of particlesizes whichis-of'interest in the particular application where this techniqueis:applied.

In accordance with the teachings'ofthe'present invention,

at any given instant of time, the cumulative percentage of solids I inthe overflow from the cyclone classifiermay bee pressed in accordancewith the following'formula:

where F I and F are in volumetric units and D and D are in specificgravity units. Experimentally the mesh number or lim'itingparticle sized corresponding to-a given F aud D, will values, measure the quantities0,, F 2 and D and calculate the corresponding values of D. These may beprinted out and/or present invention, the particle size distributionisregulated in relation to the infeed of slurry material into the grinderunit as a predetennined function of the weight of new materialintroduced into the grinder unit circuit, the known particle sizedistribution of that new material, the weight of the overflow materialfrom the classifiers returned as infeed to the grinder unit and thecalculated particle size distribution of that overflow material. v

For a more detailed understanding of the present invention both as toits organization and its method of operation together with additionalobjects and advantages thereof, reference should be made to thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a diagrammatic showing of the present control apparatus,including the condition-sensing devices, operative to determine theparticle size distribution in accordance with the teachings of thepresent invention;

FIG. 2 shows the general arrangement of a typical oregrindinginstallation and including the measurement cyclone classifier inaccordance with the teaching of the present invention;

FIG. 3 shows a curve to illustrate the technique for deter I mining thereduction modulus N and the size modulus K in accordance with thepresent invention;

FIG. 4 illustrates a modification of the particle size distributionsensing apparatus which enables the regulation of the particle sizedistribution;

FIG. 5 illustrates the additional feature of regulating the particlesize distribution of the infeed material supplied to the grinding mill;and

FIG. 6 illustrates the already well-known relationship between particlesize distribution, particle size and percentage of solids in the slurry.

in FIG. I there is shown a grinder 10 for grinding a water slurry ofmineral ore to a desired particle size for some subsequent separationoperation which is per se well known at the present time, The output ofthe grinder 10 is fed through a conduit 11, while a sample of the outputis fed to a measurement cyclone classifier 16 which is per'se well knownin the art and operative to overflow the smaller size particles ofmineral ore through an overflow outlet 18, In the overflow slurry fromthe measurement cyclone classifier 16 as supplied through conduit 18there is included a flow-sensing device 22 and a density sensing device14 from which the overflow slurry is fed bac'kto the grinder throughacon duit 26.

In FIG. I there is shown a slurry-holding tank 30 for receiving at leasta sample amount of the output slurry from the grinder 1'0 suppliedthrough conduit 32. A pump 34 is operative to pump material slurry fromthe tank 30 and supply it through the flow-sensing device '12 anddensity-sensing device I4 leading to the measurement cyclone classifierdevice 16. The: slurry pump 34 is preferably operated in a continuousmanner and should not be throttled, but rather maintains aconstant'fl'om-with the bypass valve 36 being regulated by a flowcontroller 38 as determined by the computer 46 to be operativetobypassthe undesiredportion of the mineral slurry back into the holding .tank30 as will be subsequently exhave 'been determined. The computer willset F, .at' various' flow into the measurement cyclone classifier 16.The flow controller 38 is operative with a reference flow set pointsignal supplied by the computer 46 to determine the operation of thebypass valve 36 to provide this predetermined and desired flow. Fthrough the conduit 48 leading to the measurement cycloneclassifierdevice I6. The density-sensing device I4 is operative as a transducer toprovide an output signal D, in accordance with the instantaneous densityof the slurry passing through the conduit 48.'which control signal issupplied to a density controller 44 to be compared with the referencedensity set point supplied through the input 44 for determining theoperation of the control valve 40 to regulate the instantaneous densityin terms of solids by weight in the slurry passing through the conduit48.

The computer 46 similarly receives a control signal F, in accordancewith the flow of the slurry in the overflow conduit 26 from themeasurement cyclone classifier device 16 and the density-sensing device24 provides a control signal D, to the computer 46 in accordance withthe density of the overflow slurry passing through the conduit 26 fromthe measurement cyclone classifier device 16.

The output underflow slurry flow from the fixed bottom apex valve 20 ofthe cyclone classifier device is returned to the grinder through theconduit 27. The overflow mineral slurry from the cyclone classifierdevice 16 is returned to the grinder through the conduit 26. Newmaterial is supplied to the grinder circuit through the feeder conduit50. A mixing device 52 collects the various input feeds of slurry to thegrinder l and feeds these to the grinder device 10.

In FIG. 2 the grinder is shown operative with the measurement cycloneclassifier 16 and additionally with a plurality of production of cycloneclassifiers 60, 62, 64 and 66. The measurement cyclone classifier 16 isa smaller device handling 40 or 50 gallons per minute whereas the outputfrom the grinder 10 may be in the order of a 1,000 gallons per minute orso and the production cyclone classifiers are substantially largedevices handling a much greater flow of mineral slurry for productionclassification, with the desired overflow output slurry therefrom beingpassed through the conduit 68 to a subsequent process such as awell-known flotation process to separate the mineral ore from theremaining rock and similar undesired materials.

It was known in the prior artto operate a measurement cyclone classifiermanually on a sampling basis by initially calibrating the classifier byfeeding it with slurry of a givendensity and a given velocity and thenmanually measuring the limiting particle size d of the overflow slurrythrough a mesh screen or photocell-type device or the like. Thisoperation was repeated several times to establish the relationshipbetween input slurry flow and overflow particle size. The operationcontemplated by the measurement technique of the present invention leadsitself to an online operation particle size classification installation.

In the operation of the control apparatus shown in FIGS. 1 and 2, andwith particular reference to FIG. 1, the flow controller 38 is operativeto control the valve 36 for varying the bypassof mineral slurry from theconstant speed pump 34 in a predetermined manner as determined by thecomputer 46 to set a reference inlet velocity and its corresponding flowF The computer 46 then senses the respective output control signal Ffrom the inlet flow-sensing device 12 and the control signal D, from theinlet density-sensing device 14 and the control signal F, from theoutlet flow-sensing device 22 and the control signal D, from the outletdensitysensing device 24 and calculates D in accordance with the formularelationship:

ace-w. 1( i to provide a determination of l the cumulative percentageof.

point of the flow control 38, with the density-sensing device 14 anddensity controller 42 being operative to regulate and maintain areference density set point such as 40 per cent solids by weight for themineral slurry supplied to the measurement cyclone classifier device 16through the conduit 48. In this manner a table for control operation ofthe grinder 10 may be plotted with the cumulative percentage of solids Iplotted as the ordinate versus the associated particle size d as theabscissa. With such a table any desired limiting particle sized can beobtained by a selection of the proper value of from that plotted tableand then eflecting'the necessary control of the flow controller 38 toachieve the required operation of the bypass valve 36.

In FIG. 3 there is shown a curve to illustrate the plotted relationshipof log I versus log d, where I is the cumulative percentage of solidsand d is limiting particle size. The limiting particle sizes d of eachof a given two samples are known from previous calibration and thecumulative percentage of solids I for those samples are calculated aspreviously explained. This will yield the quantities d and d as well asI and 4% for those samples.

On the resulting straight line portion of the curve 69 including points1 and 2 for the respective two samples as shown in FIG. 3, any point canbe defined according to the following equation:

when 1 100, log d= log K therefore, log 100 log K+ log C from which, logC= log 100- n log K therefore, log 1 log 100 n (log d log K) or log0/100 n log d/k Using the values 1 and :1 for sample 1 in oneapplication of the last equation and 15 and d, for sample 2 in a secondapplication of the last equation, this will provide simultaneousequations which the computer can solve for the value n, the reductionmodulus, and for the value K, the size modulus.

The value n does not change appreciably throughout the normal particlesize distribution range from a grinder for a given ore material, but thevalue K does change. The computer can use the value K determined in thismanner to provide a control signal to regulate the size of the bottomapex value of the respective production classifiers in an effort toregulate the value K to a desired and known value for correctingundesired changes in the particle size distribution from the grinderoutput. The slope of the curve 69 shown in FIG. 3 is determined by thevalues n and K with the intersection of the curve 69 being the value K.With the n not changing appreciably throughout the desired operativeparticle size distribution from the grinder 10, the value K can becontrolled between predetermined limits by the computer and in thismanner control the overflow particle size distribution from the cycloneclassifierslt is preferable that the curve 100 shown in FIG. 6 notbecome too low since the smallest particle in the overflow should not betoo small and it is also preferable that the curve 100 not become toohigh. For taconite ore, for example, percent of the material should beless than 325 mesh or 40 microns in size. By controlling K in a mannerto be later explained, the position of the curve can be maintainedwithin predetermined limits of K to yield the preferred particle sizedistribution from the grinding circuit. The following mathematicalderivation for the calculation of the-amount of solids in a mineralslurry can be utilized to derive the cumulative percentage of solidsformula as above set forth. Computer Calculation of Amount of Solids ina Slurry Let D' density of slurry (lb./ft. as measured by a gamma gaugeF volumetric flow of slurry (ft."/min.) as measured by a magnetic flowmeter.

x weight ofsolids (lbs.) per ft. slurry -y= weight of water (lbs) perft. slurry 8x density of solids lb./ft.

5y density ofwater lb./ft.

c fraction of solids by weight in slurry I00 percent= 1.0)

Thou one cu. ft. slurry, equating volumes,

K,.\' K 1 dividing by For taconite: If

Total mass flow=DF lb./min. Solids flow=CD'F lb./min. hearranging (5):

Solids flow in any slurry=(1 F =Sp. gr. then D Assuming at cyclone inletthere is a flow F and sp. gr. D and at cyclone outflow there is a flow F2 and sp. gr. 0,

la F.(D11) Then cumulative? The measurement cyclone classifier isinitially calibrated by manual experiment to determine the limitingparticle size din its overflow in relation to the inlet velocity or thedirectly related flow F.

It should be noted that the present invention is applicable to particlesize distribution control of a dry grinding process, such as ispracticed in the grinding of hematite and in the manufacture of cement.A sample is removed and fed into a container of water, and then passedthrough a measurement cyclone classifier as already described, and thenreturned to the initial container. When the density of the resultingslurry has reached some desired value, for example 60 percent solids byweight, the determination of particle size distribution can take placeas above described. The slurry is then passed back into the grindingmill. Since the flow of this slurry material will size distribution. Asshown in FIG. 4 a slurry-sampling device, such as a four" be small inrelation to the new material infeed, and considerable heat is generatedin the grinding process, no adverse effect on the moisture content ofthe raw material leaving the grinding mill will be realized. Theassociated computer can be programmed to control the sampling of thematerial to be tested into the container of water and to continu thesameuntil the resulting density of the slurry. is' as desired, :to stopthesampling and conduct the particlesize testing-by varyingthe flowrates as above described according totthe particle size being measured.The computer can be made to periodically repeat this testing .procedureon a regular basis, such -as every -5 minutes, to give a continuous andcurrent measurement of particle size distribution at the mill discharge.i

An alternative presentation of the data may be made in the form of theinstantaneous values of both size and reduction moduli current at thetime of sampling.

In FIG. 4 there is shown a modification of the slurry grinderarrangement, with atwo-way rotary valve being operative in the conduit82 to permit the slurry sample to be selectively removed from either oneof the conduits 84 and 86 as desired;

There can result under certain conditions of grinder operato provide acontrol anticipation effect, suitable control ap paratus can be providedand the computer 46 can be programmed to.vary the bottom apex values ofthe respective production classifiers 60, 62, 64 and 66 to vary theslurryun particle;

derflow therefrom and thereby control the overflow section rotatingfunnel unit 88 having one section operative to divert asample of theslurry, could be made Operative with each of the production classifiersand periodically stepped in rotary position to sample sequentially theoutput overflow slurry from a different one of the productionclassifiers, on a one-at-a time basis, such that the conduit 86 wouldthen receive the overflow slurry sample from only the production 7classifier supplying a slurry sample through the funnel unit 88 duringthe particular period of time under consideration. During the operationof the funnel unit 88, the rotary position of the funnel unit 88 isdetermined by the associated computer 46 or other suitable controller.There are many well-known position-stepping devices that would besuitable in operation to control the rotary position of the funnel unit88 as well as the position of-the valve 80 in response to a controlsignal from the associated computer 46. In conjunction with positioningthe rotating funnel unit 88 to sample the overflow output slurry from aselected one of the production classifiers, the computer 46 couldcontrol the size of the inflatable bottom apex valve of that same oneproduction classifier to vary the underflow therefrom as desired tomaintain the desired range of output particle size distribution from thegrinder apparatus shown in FIG. 4.'The size modulus K is calculated bythe computer sequentially utilized to regulate the actual size of thebottom apex from of the involved production cyclone classifi- Morespecifically, the rotary valve 80 is shown in FIG. 4 permits adetermination of the particle size distribution both before .and afterthe slurry material from the grinder passes through the productioncyclone classifiers. With the valve 80 positioned as shown in FIG. 4,the measurement cyclone classifier within the percentage ofsolids-determining apparatus 83, corresponding to the apparatus shown inFIG. 1, operates in a manner already described in relation to theshowing of FIG. I, with the conduit 82 of FIG. 4 corresponding with theconduit 32 of FIG. 1. On the other hand, with the valve 80 positioned toconnect the conduit 86 to the conduit 82, the computer 46 is instructedin its program to sequentially position the funnel unit 88 to-sar'nplethe overflow output from each respective production cyclone classifieron a one-at-atime basis and additionally to control the flow within thepercentage of solids determining apparatus to provide a first flow F,and then a second flow F,, as previously described, to permit acalculation of 9, and 11, corresponding to those two flows. With theknown limiting particle sizes d and d, relative to those provided flowsF, and F,, the particle size modulus K can be calculated as set forthregarding FIG. 3 to enable the computer 46 to regulate withinpredetermined limits the actual size of the bottom apex valve of theparticular production cyclone classifier involved. The instructionprogram of the computer 46 includes the predetermined limits for theparticle size modulus K, and the regulation of the apex valve sizeaccordingly is readily accomplished upon the calculation of the particlesize modulus K as above described. The compressed air source 45 isutilized to vary the inflation and thereby the actual size of the bottomapex valve for each production cyclone classifier in sequence.

In FIG. 5, there is an arrangement for regulating the particle sizedistribution of the infeed material supplied to the grinding mill 10.Through a mass balance technique, since the sum of the weights of thematerials leaving a given cyclone classifier in the overflow and in theunderflow is equal to the infeed of material, the computer 46 candetermine the underflow particle size distribution from the calculatedsize modulus and corresponding particle size distribution in the conduit84 leading to a cyclone classifier, such as the production cycloneclassifier 60 for example, and the calculated overflow particle sizemodulus and corresponding particle size distribution in the conduit 86leading away from the cyclone classifier. The computer 46 knows theweight W, of the underflow slurry in the conduit 85 and the weightW,+W,'of the infeed slurry in conduit 84 and the weight W, of theoverflow slurry in the conduit 86; it is per so already well known inthis particular art how to determine these weights through the use ofpresently available devices employed for this purpose. The computer 46determines the particle size distribution in the conduit 85 by solvingfor prd in accordance with the following relationship:

LKI BO'hKP M i 2) f (I ia) Now the computer 46 can control the speed ofthe motor 87 and thereby the feed of new material supplied to thegrinder 10 to regulate the particle size distribution of the slurrywithin the container 89. FIG. 6 is provided to show the presently wellknown relationship of particle size modulus K and corresponding particlesize distribution of the overflow material from a cyclone classifierillustrated by curve 100, the particle size distribution of theunderflow material per curve 102 and the particle size distribution ofthe infeed material to the cyclone classifier illustrated by the curve1045A family of these curves can be empirically determined and plottedin relation to variations of thelimiting particle size d and thecumulative percentage of solids l for a given cyclone classifier bypersons skilled in this particular art. The curve 100 has been extendedin a straight dotted line manner to indicate the size modulus K for theparticular curve 100. Assuming the slope of the curve 100 does notappreciably change for the intended particle size range of thecontrolled grinding operation, the control of this size modulus Keffectively determines the particle size distribution as desired. Thisinformation can be included in the programmed instructions given to thecomputer 46 to enable the computer to provide the desired particle sizedistribution information in relation to measured limiting particle sized and calculated cumulative percentage of solids b in accordance withthe above description.

The computer 46 can regulate the operation of the motor 87 shown in FIG.5 to maintain a predetermined particle size distribution within thecontainer 89 leading into the grinder 10, through operation of thefollowing relationship between the readily determinable quantities, theknown weight W, of new material supplied by the feed conveyor 91 drivenby the motor 87, the known weight W, of underflow slurry from thecyclone classifier 60, the known particle size distribution pad. of thenew material, such as one-fourth inch to one thirtysecond inch or thelike, and the particle size distribution psd of the underflow slurryfrom the conduit 85, and the combined weight W,,=W of the slurry withinthe container 89. The particle size distribution psd within thecontainer 89 can now be calculated by the computer 46, from thefollowing relationship:

l (P ss )+rtf p n) =W1 (P aa) and solving for psd Any difference from apredetermined or reference particle size distribution psd desired withinthe container 89 can be corrected through operation of the computer 46to vary the speed of the motor 87 and thereby to vary the feeding of newmaterial into the container 89 to hold more uniform the desired particlesize distribution within the container 89. This greatly improves theoperation of the grinder 10 in its operation to provide the desiredparticle size distribution to enhance the efficiency of subsequentmineral removal processes.

While a preferred embodiment of the present invention has beenillustrated and disclosed herein, the present invention is not to belimited thereto in that many modifications are within the scope of thepresent teachings.

lclaim:

1. In a control system for grinding apparatus supplying an output slurryto a measurement device, the combination of first means for initiallyproviding a first inlet flow operation of said slurry to saidmeasurement device and subsequently providing a second inlet flowoperation of said slurry to said measurement device, second means forestablishing a first cumulative percentage of solids in the overflowslurry leaving said measurement device during said first inlet flowoperation and for subsequently establishing a second cumulativepercentage of solids in the overflow slurry leaving said measurementdevice during said second inlet flow operation, third means forestablishing the particle size modulus of said output slurry inaccordance with a predetermined relationship between at least said firstcumulative percentage of solids and said second cumulative percentage ofsolids,

and fourth means for controlling the apparatus in accordance with saidparticle size modulus.

2. In a system for controlling the particle size distribution from agrinder supplying an output slurry to a measurement device, thecombination of means for sensing predetermined flow and densityconditions relative to a first operation of said grinder and for sensingsaid predetermined flow and density conditions relative to a secondoperation of said grinder,

means for establishing a first cumulative percentage of solids in theslurry leaving said measurement device in accordance with said flow anddensity conditions for said first operation of said grinder and forestablishing a second cumulative percentage of solids in the latter saidslurry leaving said measurement device in accordance with said flow anddensity conditions for said second operation of said grinder,

means for establishing the particle size modulus of said output slurryin accordance with a predetermined relationshipbetween said firstcumulative percentage of solids and said second cumulative percentage ofsolids,

and means for controlling the particle size distribution of said outputslurry from said grinder in accordance with said particular sizemodulus.

3. In a control system for a grinding device supplying an output slurryto a classifier device, the combination of,

first means operative with said output slurry from the grinding devicefor determining at least one of a first flow characteristic and a firstdensity characteristic of the slurry supplied to said classifier device,

second means operative with the slurry leaving said classifier devicefor determining at least one of. a second flow characteristic and asecond density characteristic of the slurry leaving said classifierdevice, third means operative with said first and second means forestablishing the percentage of solids relationships in said outputslurry in accordance with a predetermined relationship between at leastsaid one of said first flow characteristic and said first densitycharacteristic and said predetermined relationship between at least saidone of said second flow characteristic and said second densitycharacteristic,

' and control means operative to control the operation of said grindingdevice in accordance with said percentage of solids relationship.

4. The control system of claim 1 with said measurement device being ameasurement cyclone classifier and with said grinding apparatusincluding a production cyclone classifier, with said measurement cycloneclassifier being operative with the output slurry from the grindingapparatus which appears in the overflow slurry from said productioncyclone classifier,

and with said third means for establishing the particle size modulusbeing operative in relation to the percentage of solids in the overflowfrom said production cyclone classifier.

5. The control system of claim 3, with said grinding device having aportion of said output slurry returned to said grinding device andincluding a new material supply,

with said third means being operative to determine the particle sizedistribution in at least the slurry returned to said grinding device andwith said control means being operative to control said new materialsupply to maintain a predetermined particle size distribution in theslurry supplied to said grinding device.

6. The control system of claim 1, with said grinding apparatus includinga plurality of production cyclone classifiers, said combinationincluding overflow slurry sampling means operative to supply said outputslurry to said measurement device for sequentially sampling the overflowslurry from each one of the respective production cyclone classifiers,

and with said fourth means being operative in response to said particlesize modulus to control the particular production cyclone classifierbeing sampled.

7. The method of controlling a grinding system including a grindingdevice connected to supply an output slurry to a classifier device, thesteps of determining a first flow and a first density of the slurryleading to said classifier device,

determining a second flow and a second density of the slurry leavingsaid classifier device, 1 establishing the particle size modulus of saidoutput slurry in accordance with a predetermined relationship betweensaid first and second flow and said first and second densiandcontrolling the particle size distribution of said output slurry inresponse to said particle size modulus.

8. The method of claim 7 with said classifier device being a measurementclassifier device and with said grinding system including a plurality ofproduction particle size classifiers, said method including the steps ofv determining in sequence the particle size modulus of a trample of theoutput slurry from each selected one of the respective productionclassifiers,

and controlling the particle size distribution of the output slurry fromthe selected production classifier correspond-.

ing with the particular sample for which the particle size modulushas'been determined.

9. In a control system for a grinding device connected to supply anunknown slurry to a classifier device having an output slurry, thecombination of first flow-sensing means and first density-sensing meansoperative with the unknown slurry from the grinding mill for determiningrespectively the inlet flow F, and the inlet density D, of the slurrysupplied to said classifier device,

second flow-sensing means and second density-sensing means operativewith the output slurry of said classifier device for determiningrespectively the output flow F and the output density D of the outputslurry of said classifier device,

third means operative with said flow and density sensing means forestablishing a percentage of solids relationship D in said output slurryin accordance with the predetermined formula and control meansresponsive to said percentage of solids l in accordance with formula forcontrolling of operation of said grinding device to provide a desiredoperation of said grinding device.

10. The control system of claim I, with said measurement device being ameasurement cyclone classifier, with said grinding apparatus beingoperative with a production cyclone classifier, and with saidmeasurement cyclone classifier being operative with said output slurryfrom the grinding apparatus which appears in the overflow slurry fromsaid production cyclone classifier, the combination including said thirdmeans being further operative to calculate the particle size modulus inrelation to the particle size distribution in said overflow slurry,

and with said fourth means being responsible to said particle sizemodulus to control the particle size distribution from said grindingapparatus.

11. The control system of claim 1, with said grinding apparatus having aportion of said output slurry returned to said grinding apparatus andincluding a new material supply,

with said third means being further operative to determine the particlesize distribution in at least said output slurry returned to saidgrinding apparatus and being operative to control said new materialsupply to maintain a predetermined particle size distribution in saidoutput slurry from said grinding apparatus.

12. The control system of claim 3, with said grinding device including aplurality. of production cyclone classifiers, said combination includingoverflow slurry sampling means operative with said first means forsequentially sampling the overflow slurry from each one of therespective production cyclone classifiers,

and with said control means being operative to control the particle sizedistribution of the particular production cyclone classifier beingsampled.

13. The method of controlling a grinding system connected to supply anoutput slurry to a-classifier device, the steps of determining at leastone of the flow and density of the slurry leading to said classifierdevice,

determining at least one of the flow and density of the slurry leavingsaid classifier device,

establishing the particle size modulus of said output slurry,

and controlling the particle size distribution of said output slurry inresponse to said particle size modulus.

14. The method of claim 13 with said classifier device being ameasurement classifier device and with said grinding system includingaplurality of production particle size classifiers, said method includingthe steps of determining in sequence the particle size modulus of asample of the output slurry from each one of the respective productionclassifiers and controlling the particle size distribution of the outputslurry from each one of said production classifiers in sequence beforeperforming the same operation on a sample of the output slurry from thenext sequence production classifier.

2. In a system for controlling the particle size distribution from agrinder supplying an output slurry to a measurement device, thecombination of means for sensing predetermined flow and densityconditions relative to a first operation of said grinder and for sensingsaid predetermined flow and density conditions relative to a secondoperation of said grinder, means for establishing a first cumulativepercentage of solids in the slurry leaving said measurement device inaccordance with said flow and density conditions for said firstoperation of said grinder and for establishing a second cumulativepercentage of solids in the latter said slurry leaving said measurementdevice in accordance with said flow and density conditions for saidsecond operation of said grinder, means for establishing the particlesize modulus of said output slurry in accordance with a predeterminedrelationship between said first cumulatiVe percentage of solids and saidsecond cumulative percentage of solids, and means for controlling theparticle size distribution of said output slurry from said grinder inaccordance with said particular size modulus.
 3. In a control system fora grinding device supplying an output slurry to a classifier device, thecombination of, first means operative with said output slurry from thegrinding device for determining at least one of a first flowcharacteristic and a first density characteristic of the slurry suppliedto said classifier device, second means operative with the slurryleaving said classifier device for determining at least one of a secondflow characteristic and a second density characteristic of the slurryleaving said classifier device, third means operative with said firstand second means for establishing the percentage of solids relationshipsin said output slurry in accordance with a predetermined relationshipbetween at least said one of said first flow characteristic and saidfirst density characteristic and said predetermined relationship betweenat least said one of said second flow characteristic and said seconddensity characteristic, and control means operative to control theoperation of said grinding device in accordance with said percentage ofsolids relationship.
 4. The control system of claim 1 with saidmeasurement device being a measurement cyclone classifier and with saidgrinding apparatus including a production cyclone classifier, with saidmeasurement cyclone classifier being operative with the output slurryfrom the grinding apparatus which appears in the overflow slurry fromsaid production cyclone classifier, and with said third means forestablishing the particle size modulus being operative in relation tothe percentage of solids in the overflow from said production cycloneclassifier.
 5. The control system of claim 3, with said grinding devicehaving a portion of said output slurry returned to said grinding deviceand including a new material supply, with said third means beingoperative to determine the particle size distribution in at least theslurry returned to said grinding device and with said control meansbeing operative to control said new material supply to maintain apredetermined particle size distribution in the slurry supplied to saidgrinding device.
 6. The control system of claim 1, with said grindingapparatus including a plurality of production cyclone classifiers, saidcombination including overflow slurry sampling means operative to supplysaid output slurry to said measurement device for sequentially samplingthe overflow slurry from each one of the respective production cycloneclassifiers, and with said fourth means being operative in response tosaid particle size modulus to control the particular production cycloneclassifier being sampled.
 7. The method of controlling a grinding systemincluding a grinding device connected to supply an output slurry to aclassifier device, the steps of determining a first flow and a firstdensity of the slurry leading to said classifier device, determining asecond flow and a second density of the slurry leaving said classifierdevice, establishing the particle size modulus of said output slurry inaccordance with a predetermined relationship between said first andsecond flow and said first and second density, and controlling theparticle size distribution of said output slurry in response to saidparticle size modulus.
 8. The method of claim 7 with said classifierdevice being a measurement classifier device and with said grindingsystem including a plurality of production particle size classifiers,said method including the steps of determining in sequence the particlesize modulus of a sample of the output slurry from each selected one ofthe respective production classifiers, and controlling the particle sizedistribution of the output slurry from the selected productionclasSifier corresponding with the particular sample for which theparticle size modulus has been determined.
 9. In a control system for agrinding device connected to supply an unknown slurry to a classifierdevice having an output slurry, the combination of first flow-sensingmeans and first density-sensing means operative with the unknown slurryfrom the grinding mill for determining respectively the inlet flow F1and the inlet density D1 of the slurry supplied to said classifierdevice, second flow-sensing means and second density-sensing meansoperative with the output slurry of said classifier device fordetermining respectively the output flow F2 and the output density D2 ofthe output slurry of said classifier device, third means operative withsaid flow and density sensing means for establishing a percentage ofsolids relationship phi in said output slurry in accordance with thepredetermined formula and control means responsive to said percentage ofsolids phi in accordance with formula for controlling of operation ofsaid grinding device to provide a desired operation of said grindingdevice.
 10. The control system of claim 1, with said measurement devicebeing a measurement cyclone classifier, with said grinding apparatusbeing operative with a production cyclone classifier, and with saidmeasurement cyclone classifier being operative with said output slurryfrom the grinding apparatus which appears in the overflow slurry fromsaid production cyclone classifier, the combination including said thirdmeans being further operative to calculate the particle size modulus inrelation to the particle size distribution in said overflow slurry, andwith said fourth means being responsible to said particle size modulusto control the particle size distribution from said grinding apparatus.11. The control system of claim 1, with said grinding apparatus having aportion of said output slurry returned to said grinding apparatus andincluding a new material supply, with said third means being furtheroperative to determine the particle size distribution in at least saidoutput slurry returned to said grinding apparatus and being operative tocontrol said new material supply to maintain a predetermined particlesize distribution in said output slurry from said grinding apparatus.12. The control system of claim 3, with said grinding device including aplurality of production cyclone classifiers, said combination includingoverflow slurry sampling means operative with said first means forsequentially sampling the overflow slurry from each one of therespective production cyclone classifiers, and with said control meansbeing operative to control the particle size distribution of theparticular production cyclone classifier being sampled.
 13. The methodof controlling a grinding system connected to supply an output slurry toa classifier device, the steps of determining at least one of the flowand density of the slurry leading to said classifier device, determiningat least one of the flow and density of the slurry leaving saidclassifier device, establishing the particle size modulus of said outputslurry, and controlling the particle size distribution of said outputslurry in response to said particle size modulus.
 14. The method ofclaim 13 with said classifier device being a measurement classifierdevice and with said grinding system including a plurality of productionparticle size classifiers, said method including the steps ofdetermining in sequence the particle size modulus of a sample of theoutput slurry from each one of the respective production classifiers andcontrolling the particle size distribution of the output slurry fromeach one of said production classifiers in sequence before performingthe same operation on a sample of the output slurry from the nextsequence production classifier.